Client

BKW Energie AG

The 1,097 MW power plant went into commercial operation in 1971 and consists of a single-unit boiling water reactor. The owner/operator of the Mühleberg Nuclear Power Plant (KKM) needed to submit an updated Level 1 probabilistic safety assessment (PSA) to the Swiss nuclear regulator. SGH developed seismic fragilities of essential structures, systems, and components (SSCs).

Scope | Solutions

Essential safety systems are contained in several buildings. Within the reactor building, the reactor vessel is enclosed by a light bulb-shaped steel drywell connected to a torus-shaped primary suppression chamber supplemented by a secondary suppression chamber. SGH developed seismic fragilities for SSCs, an essential element of the updated seismic PSA. Earthquake ground motion was based on the most recent site-specific seismic hazard. For this project, SGH:

Carried out a seismic walkdown of SSCs per EPRI NP-6041-SL

Developed a database to document the seismic walkdown

Performed probabilistic seismic response analysis of the structures to obtain probability distributions of seismic forces and in-structure response spectra

Analyzed soil-structure interaction effects for the KKM structures using CLASSI and SASSI software

Developed the seismic fragilities of numerous SSCs per EPRI TR-103959 and EPRI TR-1002988 recommendations

Used nonlinear analysis in combination with Latin Hypercube Sampling to develop the seismic fragility evaluation of structures

Developed seismic fragilities of essential underground piping systems for displacements due to soil liquefaction

Extended the seismic fragility evaluation to address the plant seismic risk during an outage

Performed seismic walkdowns to identify seismic-fire and seismic-flood interactions